Limb position sense (LPS) is the ability to sense the movement and position of limbs in space. During locomotion, limb position sense is regulated by sensory feedback to the nervous system from proprioceptors, which include cutaneous, vestibular, muscle and joint receptors. Such proprioceptors respond to locomotion and provide the information needed to know the position of a subject""s limb(s) in space. (Williams W J. A systems-oriented evaluation of the role of joint receptors and other afferents in position and motion sense. CRC Critical Reviews in Biomedical Engineering. 1981; 7:23-77.)
Proprioceptive feedback from muscle, joint and cutaneous receptors are essential for the generation of the normal motor pattern. (Gandevia S C, Burke D. Does the nervous system depend on kinesthetic information to control natural limb movements? Behavioral and Brain Sciences. 1992;15:614-632.) Neural stimulation detected by receptors travels to the central nervous system for integration via cortical and reflex pathways. These mechanoreceptors demonstrate adaptive properties depending on a particular stimulus. Pacinian corpuscles are quick adapting joint mechanoreceptors that decrease their discharge rate to extinction within milliseconds of the onset of a continuous stimulus. It is postulated that they mediate the sensation of joint motion because they are sensitive to changes in position. Slow-adapting mechanoreceptors, including muscle spindle, Golgi tendon organ and Ruffini ending joint receptors, are thought to mediate the sensation of joint position and changes in position because they are maximally stimulated at specific angles. (Lephart S M. Proprioception following ACL reconstruction. J Sports Rehab. 1992; 1:186-196.) Muscle spindle receptors are found within skeletal muscle and function to measure tension upon stretch of the muscle. Golgi tendon organs are located at the musculotendinous junction and function as a protective mechanism by inhibiting the motor neurons innervating the muscles that were stretched while exciting the motor nerves of the antagonistic muscles.
Various studies have also confirmed the role of these receptors in providing information to the central nervous system about tissue deformation. Other studies by Goodwin et al and Eklund showed that perception of limb position sense and movement is derived from muscle spindle. (Gandevia S C, Burke D. Does the nervous system depend on kinesthetic information to control natural limb movements? Behavioral and Brain Sciences. 1992; 15:614-632.) In their studies, when vibration was applied to muscles, tendon movement occurred. Direct recordings from human spindle afferents suggest that these movements depend upon signals from primary and secondary spindle endings. Hiebert et al indicated that proprioceptors that signal hip extension might arise from muscle spindle afferents. (Hiebert G W, Whelan P I, Prochazka A, Pearson K G. Contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat step cycle. J Neurophysiol. 1996; 75:1126-1137.) Gandevia and Burke, supra, demonstrated that acuity can be diminished with both cutaneous and joint anesthesia, particularly in joints in the hand.
Perception of afferent signals, however, is not required for movement. The spinal cord has complex neural circuitry, which is capable of producing rhythmic, oscillating commands to the musculature, even in the absence of sensory input. Central motor programs alone are sufficient to control simple learned movements. For example, Gandevia et al, supra, showed that subjects can recruit and grade the motor drive to a paralyzed muscle in the absence of feedback from that muscle. Grillner et al described research performed on animals (Grillner S. Locomotion in vertebrates: Central mechanisms and reflex interaction. Physiol Reviews. 1975; 55:247-304): The spinal cord of cats is cut at a level below the brain so that the higher centers cannot influence lower ones, and the cord is deafferented below the level of the cut. When the cord is stimulated, the cat produces stepping movements that resemble normal locomotion in cats without feedback from the limbs.
Afferent feedback, however, is critical in providing the central nervous system with input, especially when involving small, precise contractions during phase transitions or disturbances. Afferent signals, for example, are required to modulate the central pattern generator of the locust and thus for its nervous system to generate the appropriate motor pattern. When deafferented, the locust cannot maintain the normal flight rhythm despite a wind stimulus to its head. The authors explain that the change in flight behavior is associated with significant changes in the profile of synaptic activation in many interneurons in deafferented preparations and with alterations in the motor pattern.
Feedback during active and passive movements is more functional than during static positioning. Studies using microneurography of the human hand during active and passive movement show a response from cutaneous, joint and muscle afferents. During both active and passive movements, the majority of afferents from all classes of cutaneous receptors alter their discharge rates. In a static position, however, there is little background discharge in any of the cutaneous receptors. (Gandevia S C, Burke D. Ibid.)
In a review article spanning the past 20 years, Duysens and colleagues show the importance of proprioceptive feedback in triggering events in the gait cycle. (Duysens J, Clarac F, Cruse H. Load-regulating mechanisms in gait and posture: Comparative aspects. Physiol Reviews. 2000; 80:83-133.) They discuss research with spinal cats on a treadmill whereby they found that at end stance the cat""s limb is extended and unloaded whereas at end swing the cat""s limb is flexed and beginning to unload. Researchers then questioned what triggered these transitions. They postulated that the transition from stance to swing was triggered by load and the transition from flexion to extension was triggered by limb position sense.
Afferent feedback provides information about human movement and can influence normal movement. Sharma et al studied knee joints with and without osteoarthritis and identified two possible directions in the relationship between impaired proprioception and knee osteoarthritis: 1) that proprioceptive impairment contributes to the development of knee osteoarthritis; or 2) that knee position sense impairment results from osteoarthritic pathologic processes at the joint. (Sharma L, Pai Y-C, Holtkamp K, Rymer W Z. Is knee joint proprioception worse in the arthritic knee versus the unaffected knee in unilateral knee osteoarthritis? Arthritis and Rheumatism. 1997; 40:1518-1525.) They concluded that within the patients with osteoarthritis, proprioception was not worse in the arthritic knees than in the unaffected knees. These results suggest that impaired proprioception is not exclusively a local result of disease in knee osteoarthritis; rather, impaired proprioception may contribute to knee osteoarthritis.
LPS activity is measured in order to determine if a person is capable of accurately placing a limb in key positions during functional movements. Clinical measurement of proprioception is currently, in the prior art, determined by two methods: 1) single joint position placement and/or 2) mirroring. In the former, the therapist places a limb in either flexion or extension and the patient verbally indicates the position of his/her limb or duplicates the position with the contralateral limb. In the latter, the patient mimics the movement of the therapist and attempts to mirror that same movement with the contralateral limb. Also, movement detection is tested by slowly moving the limb until the person indicates a sense the limb is moving. These are static, single joint measurements that do not signify how proprioception effects movementxe2x80x94contrary to the above-cited research which indicates that limb position sense becomes more acute with active movement and with multisegmental joint movement.
As such, the techniques of the prior art do not directly test a person""s ability to sense limb position during an ongoing functional movement. Likewise, the prior art does not test LPS acuity during different phases in the trajectory of the movement. It has been shown by previous researchers that proprioceptive input from peripheral receptors are activated differently during different phases of a movement cycle. Also, studies have shown that the central nervous system processes the peripheral input differently at different points in a movement trajectory. Other studies have shown that LPS is altered during movement compared with static or near static positioning tasks. Ongoing movement may alter the peripheral input so that LPS acuity is altered with movement.
The present invention is concerned with limb position sense as it pertains to locomotion, specifically, but not limited to, cyclic movement. Thus, an object of this invention is to assess or determine if limb position sense is more accurate during multijoint movement and phase transitions and to provide rationale for a clinical evaluation tool that more accurately measures limb position sense. It would be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all its respects, to every aspect of this invention. As such, any one object can be viewed in the alternative with respect to any one aspect of this invention.
Related objects of the invention provide for a method and/or apparatus to test and prove two hypotheses: 1) that limb position sense will be enhanced with movement versus nonmovement conditions; and 2) that enhancement of limb position sense will be phase specific with greatest enhancement occurring at the two transition phases between flexion and extension. As demonstrated below and meeting such objects, limb position sense measurements as used in the clinic can become more valid with respect to functional movement.
It can be an object of the present invention to provide broad methodologies and/or systems and apparatus useful therewith to assess or improve position sense during repetitive movement, such position sense as it relates to the repetitive movement of a subject""s arms, legs, hands or feet.
It can also be an object of the present invention to provide a clinical test or evaluation revealing impairments in the ability to sense limb position during movement, such that such results can be taken into account in evaluating a variety of locomotor tasks.
It can also be an object of the present invention to provide a general method for the determination or assessment of position sense such that the results obtained thereby can be communicated to an individual subject to improve use or perception of existing proprioceptive signals during movement.
It can also be an object to effect the methodologies of this invention through use of a system, apparatus and/or components other than those described herein, such components as would be well-known to those skilled in the art made aware of this invention, such components as could be obtained through straight-forward modifications of currently available components and/or apparatus, consistent with the broader teachings disclosed herein or otherwise in accordance with this invention.
Other objects, features, benefits and advantages of the present invention will be apparent from the following summary and detailed descriptions of various preferred embodiments, and would be readily apparent to those skilled in the art having knowledge of various limb position sensing technologies. Such objects, features, benefits and advantages will be apparent from the above as taken in conjunction with the accompanying examples, studies, data, figures and all reasonable inferences to be drawn therefrom, alone or in consideration with their departure from the prior art.
This invention is a novel application, both by way of methodology, system and apparatus, of limb position sense testing or assessment or determination. In preferred embodiments, individuals are asked to indicate, verbally, when they feel that their leg or arm, for example, has passed through a particular target point during cyclical movement. The verbal indication is recorded and the actual position of the limb, measured by an encoder or potentiometer, is compared to the expected target position. The error in judgement is used as an indicator of functional movement impairment during such tasks as walking, reaching, and standing up from a chair. Unlike the prior art, this invention measures limb position acuity and/or impaired locomotion during an ongoing movement rather than after the movement has stopped. Also, because limb position sense is thought to alter dependence on the particular phase of the movement trajectory, traditional methods are not valid indicators of how limb position sense is used during an ongoing movement task.
The method and/or apparatus of this invention enables clinicians, for the first time, to match limb position sense acuity to actual functional movements and, therefore, better to predict actual deficits in behavior. In various preferred embodiments, this invention can also be used as an intervention (e.g., xe2x80x9cfeedbackxe2x80x9d) to train individuals to improve limb position sense during an ongoing movement, such intervention as can be accomplished through the provision, to a subject individual, comparative information regarding actual and selected positions.
In preferred embodiments, this invention can be practiced using a modified standard pedaling ergometer (either arm or leg). The standard ergometer can be equipped with a potentiometer or optical encoder that is placed at the center of crank rotation so as to precisely measure crank position. By way of example, a subject is given a microphone connected to a circuit that can generate voltage signals upon voice activation. The subject is instructed on the different positional targets of interest during the test. The subject is blindfolded, then asked to pedal slowly as the tester tells the individual to say a predetermined word xe2x80x9cBobxe2x80x9d loudly and clearly as soon as he/she feels as if they have passed over the indicated target. The subject can repeatedly attempt to identify the target on multiple cyclic repetitions. Each time the subject indicates they have hit the target, a signal is generated that matches a particular crank position. A small processing unit can calculate the difference between the actual voice indicated position and the expected target position. Once calculated, the error measurement can be used to compare the subject""s performance with normative values and also to indicate points in the movement trajectory where acuity is particularly impaired. Other apparatus/components providing similar function and effectxe2x80x94all of which can comprise commercially available componentsxe2x80x94would be apparent to those skilled in the art made aware of this invention.
As mentioned above, the invention may also be applied as an intervention. For example, as the person is cycling, he can be provided with corrective feedback about how close or far away from the expected target he was, by way of learning how to use existing proprioceptive signals, to detect important phases of the movement cycle. Accordingly, in certain embodiments, the system, components and/or apparatus of this invention can be employed as an xe2x80x9cadd-onxe2x80x9d to any existing leg or arm powered ergometer, for use by neurologists, physical therapists, occupational therapists, health screeners, nurses, etc., again, as either a screening device or as an intervention to improve limb position sense during movement.
In light of the above and as provided elsewhere herein, the present invention is, in part, a method of assessing limb position sense accuracy. The method includes: (1) providing a test subject engaged in a repetitive movement having a trajectory with a plurality of positions thereon, the method including, but not limited to, movements of upper limbs, lower limbs, feet and hands, or a combination thereof, the subject having a particular body orientation and/or posture during the engaged movement; (2) selecting a position on the movement trajectory; (3) recording the actual position sensed by and indicated by the subject responsive to the selected position; and (4) comparing the indicated actual position with the selected position. In various preferred embodiments, the comparison or difference between indicated actual position and selected position can be provided as information to the subject during the engaged repetitive movement, as a feedback or intervention mechanism to improve use of existing proprioceptive signals and resulting limb position sense accuracy.
In various preferred embodiments, the engagement is repetitive lower limb movement, regardless of whether such movement is active, passive or has a load applied thereto. With respect to the latter variable, a variety of weighted loads or resistive forces can be applied against the repetitive movement and, hence, the limb engaging therein, so as to further assess position sense or a subject""s acuity thereof.
In various other preferred embodiments, alone or in conjunction with any of the above, limb movement, whether upper or lower, can further include coincidental contralateral limb movement. For example, in the context of repetitive lower limb movement, both limbs can move together, whether in phase or out of phase one with one another. With respect to the former, both limbs can move along the same trajectory at the same time. Conversely, with respect to the latter, both limbs can move in the same trajectory at different times up to 180 degrees out of phase (i.e., where one leg is flexing while the other leg is extending). In such a manner, the present methodology can be used to assess the affect of one leg on the other during movement, as an influence on limb position sense and/or the accuracy thereof. In various other embodiments, it can be preferable to engage only one limb in repetitive movement so as to assess position sense without input from the contralateral limb.
Likewise, in preferred embodiments of the present methodologies, an especially useful repetitive movement is cyclic pedaling, an activity having various components which together simulate a walking movement. Inasmuch as limb position sense can vary depending upon rate or velocity of movement, such activities are preferably engaged at a constant rate. While preferred such methods and cyclic repetitive movements are described in conjunction with lower limb position sense, this invention in its broader aspects also contemplates various other embodiments corresponding to upper limb movement. Accordingly, a variety of components, apparatus and/or systems of the type described herein can be modified to accommodate such repetitive movement, simulating common human locomotion, not only with respect to upper and lower limbs, but also the extremities (hands and feet) thereof.
As such, the present invention also includes, in part, a system for assessing limb position sense accuracy and/or acuity during ongoing movement. Such a system includes: (1) a movement trajectory component; (2) a subject position indicator; and (3) a comparative measurement component. Various preferred system embodiments are described in more detail below in the context of angular motion. However, this would be apparent to those skilled in the art made aware of this invention, the present methodologies, components and/or systems can be applied with comparable benefit to various linear motions or combined angular/linear motions. As such, the associated movement trajectories include those of a subject""s arms, legs, hands and/or feet, depending upon repetitive movement selected.
Nonetheless, in the preferred embodiments, for reasons described above, the repetitive movement is the angular motion of a cycling activity, as can be effected through use of a pedaling ergometer. Optionally, such a component can further include a potentiometer to measure pedal crank position along the movement trajectory. Various other embodiments of such a component can make effective use of well-known optical or visual tracking devices. Regardless, the indicator component is preferably a subject-activated physical signal. In highly preferred embodiments, such a subject position indicator is a voice-activated electrical signal, such as that available through use of a microphone, so as to avoid other limb or extremity contact and implication of associated proprioceptive factors.
Movement trajectory position and subject-indicated position data can be comparatively processed and/or evaluated to determine differences there between various such data processing components would be well-known to those skilled in the art made aware of this invention, and could be incorporated into the present apparatus and/or system in a straightforward fashion.